Improving Horses and Mules

Improving Horses and Mules By J. O. Williams, Senior Animal Hus-^ handman^ and William Jac\son, Associate Animal Husbandman^ Bureau of Animal Industry THE breeding of horses is an art that goes far back in history. No animal, with the possible exception of the dog, has had so much affection and respect from man as the horse, and it is safe to say that few possessions are more cherished than a fine horse. The desire to breed better animals has been correspondingly strong, and much lore about horse breeding has developed during many generations. For reasons that will be made plain in this brief surve}^^, however, the new science of genetics has as yet achieved little in this field. No attempt is made here to record the history of horse breeding, but only to sum up certain aspects of the situation from the scientist's viewpoint. In order to show what progress has been made in the fixation of inheritance for various chara.cters in horses, the cooperation of each State agricultural experiment station was asked to obtain certain breeding information on outstanding individuals and studs. The points upon which data were requested included: For draft breeds— plan of breeding, services per mare and foals produced, weight at birth, measurements at birth, ages when subsequent measurements are taken, height, temperament, action, muscling, strength, stamina, s^^mmetry of conformation, feed consumption, and soundness; for light breeds—plan of breeding, services per marc and foals produced, weight at birth, measurements at birth, when subsequent measurements arc taken, height, temperament, action, symmetry of conformation, speed, gaits, length of neck, slope of shoulder, length of pastern, shape of foot, set of legs, quality of bone, and soundness. In addition each station was asked: (1) Whether a progeny-testing method was used; (2) to submit a list of horse-breeding project activ- ities; and (3) to submit names and addresses of owners of studs having a reputation for developing superior breeding stocks. With this information it would be [possible to summarize the research achieve- ments in the field of horse breeding as a background for the develop- ment of well-rounded plans for further investigation. 929 The Status of Scientific Wor\on Inheritance in Horses THE questionnaires indicate that 18 States are doing no work in horse breeding, while 21 States maintain studs, usually for class- room work. Percherons were found in most of these, Belgians in manjr of them, Clydesdale and Thoroughbreds each in two, and Arabian horses in one. Nine States made no report. Few of these States have experimental projects that involve a distinct genetic approach to horse breeding. The work being done either concerns the ph3^siolog3^ or pathology of reproduction in con- nection with college work, or the recording of limited data. Colts are weighed at birth and at more or less regular intervals thereafter. A few stations record height at withers and some record heart girth (circumference of chest), circumference of fore and hind cannon bones, color, markings, and such data as mating and foaling dates and feed and work records. Much more is known, of course, about the horses in a stud than is indicated in the recorded data. Many of them are studied and judged critically by classes in animal husbandry, and the peculiar- ities of their form, action, and temperament are known to instructor and student. A few stations conduct experiments aimed largely at finding out the cost of producing colts. Such stations record feed consumption and other costs, but primarily for the information this will give on management methods. Also, some stations reported records that yield information about the breeding efficiency of their stallions and mares. On the average, two services are required for each colt produced. A BRIEF REVIEW OF RESEARCH IN HORSE BREEDING A survey of the literature reporting current and recent research work with horses reveals a considerable number of experiments on the physiology of mating and reproduction, particularly in the United States, Great Britain, the Union of Soviet Socialist Republics, Germany, France, and Japan; several experiments for improving technique in the practice of artificial insemination; a few studies of the inheritance of color; an occasional one attempting to correlate body measurements or other factors with constitution and performance ; and one study of blood groups in the horse and their inheritance. Hart and Cole (lOy of the California Agricultural Experiment Station have developed a method for diagnosing pregnancy in mares as early as 42 days after breeding that is sufficiently practical for use by stables where intensive breeding of valuable horses is being done. By its use it should be possible greatly to reduce the uncertainty and waste of time in establishing whether a mare has been successfully bred. It should also be valuable in obtaining an early indication of a new stallion's abihty to get foals. Other workers {8, 9, 13j 15) have made additional contributions to that of Hart and Cole. 1 italic numbers in parentheses refer to literature cited, p. 945. 930 Two workers (2) of the Union of Soviet Socialist Republics dem- onstrated that gravidan, a hormone obtained from the urine of the pregnant mare, is of practical use in inducing ovulation in mares that have previously failed to come into heat or refused to accept the male. Eickman (6), in Germany, estimated that of 20,000 mares served in the Rhine Province during 1934, as many as 8,000 required treatment for sterility. In approximately 1,000 tests for diagnosis of pregnancy—blood tests from the forty-ninth to the one hundred and FIGURE l.—The versatile American farmer is learnins; to use iiis horse power in larger units to save man labor and perform the heavy operations on farms such as plowing. This is an eight-horse hitch pulling a three-bottom gang plow. A horse must have the proper temperament to work well in the various types oí hitches. fiftieth day and urine tests thereafter—the percentage of error was 0.9; while 39 percent of the sterile mares yielded to treatment and foaled. An attempt to measure racing capacity in the Thoroughbred horse has recently been made by Laughlin (14) of the Carnegie Institution of Washington, and after several years' work on the problem he has devised a basic formula by which racing capacity may be measured 931 within certain limits, and niatbematical rules that apparently govern its inheritance. Stone {19) of Stanford University, after weighing many lines of evidence, advanced the belief that male Thoroughbred horses as a class surpass the females of that breed in running abihty, and that the best of the females are inferior to the best of the males in this respect. Müller (Í7) in Germany found, after extensive study, that chest length, width, depth, and girth measurements do not give an indication of performance in terms of speed and endurance in horses, be- cause they do not reliably indicate the volume of the thorax or of the vital organs located there. He found some indication of an interrela- tion in some of these factors—that chest length, for example, is greater in light and riding horses than in heavy draft-type horses. In a study (ii?) of the significance of shoulder measurements in rela- tion to running performance, Müller also summarized the results of some 20 others, adding a tabulation of his own of some 200 animals. He could find in shoulder measurements no reliable sign of running performance, and concluded that the systems of judging frequently recommended have no scientific basis. Another German worker, Kaempñer {12), reports extensive studies of blood groups in the horse and their inheritance, and found it possible successfully to diagnose paternity in 22 cases out of 82 at- tempted, on the basis of new agglutinogens which he has demon- strated. THE NEED FOR UNIFORM DEFINITIONS OF CHARACTER AND PERFORMANCE On the whole, little definite knowledge exists on the genetics of the horse (^, 18), although he has been bred to greater variety than most other classes of Hvestock. For instance, coat colors in horses range through many conabinations and a number of puzzling degrees of intensity not readily discernible or capable of being expressed in definite terms. In all breeds except the Suffolk, which must^ be chestnut, there are found most of the usual horse colors, which would indicate that most breeds are heterozygous for color and that most individual horses are heterozj^gous for one or more of the several genes having important effects on color. Furthermore, although speed and amount of work performed are readily measurable quanti- ties, there is such a lack of satisfactory measures and expressions of a horse's will to perform to the maximum of his abihty, the suit- ability of his nervous temperament for the duties demanded of him, and the part that his training may have played in influencing his inherited abihties, that the geneticist is greatly handicapped in his analysis. These needs, together with the relatively high cost of the horse as experimental material and his slowness to reach maturity, have pre- vented finding very definitely what are the correlations between characteristics and performance. Of cattle we demand meat and milk; of sheep, meat and wool. But of horses we ask power, versatihty, speed, endurance, beauty of form and of action, courage, intelligence, and intuition in an amazing variety of combinations—hence the different types, conformations, weights, dispositions, and even colors to be found in the form of 932 horse flesh. The range runs from the plump, docile Shetland pony, or the harness pony 36 to 40 inches in height, weighing 500 pounds or less and possessing graceful, rhythmic action, to the ponderous draft horse standing 70 or more inches in height and weighing a ton and upwards.

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